Support tracking files through log rotation events instead of requiring static extensions in config.

[abraithwaite]

Right now, we require a static extension for the file source to prevent the following scenario:

• logrotate creates a new file with different extension from the original
• our file source sees the new file and starts consuming it
• it's already consumed those logs.

Currently we prevent this by assuming that logrotate is appending a different extension onto the files (suchas .1 or .gz).

Ideally, we could watch an entire directory and collect all the logs without having to resort to filtering down to a specific extension.

Also, we may run into issues where logrotation inserts a file modification as .1.log or something like that which is still unhandled and would result in duplicate logs.